JP Barrels accuracy

[KZero]

but that black teflon is outside; however, what coating is inside?

(for example Faxxon offers inside and outside nitride salt bath coating, which i assume helps from corrosion greatly)

The barrel you linked to is 416R stainless; it's unlikely to need any coatings on the inside, a process normally associated with harder-use/high-volume-in-a-short-time types of use. Most accuracy-oriented shooters don't want anything inside their bores.